Tending the tiller or wheel of a boat, even a small one, can be a boring and tiresome job. To alleviate that situation, a variety of automatic steering control systems have been devised. They all include some means for establishing a desired course heading, and they include a direction sensing device.
Early automatic steering systems were developed for larger vessels in servo-mechanism form. The feedback systems were quite complex and costly. In any event, they were too complex and costly for use on smaller boats.
The current standard for small boats is a simple servo-mechanism. One of the most popular and successful, at least for direct control of the tiller, is a servo-mechanism whose error detector includes a compass whose card is mounted for rotation in a compass case which is itself mounted for rotation relative to the vessel's heading. The compass card is opaque over half of its area or circumference and clear or reflective over the other half. A sensor mounted for rotation with the compass case relative to the card distinguishes opaque from reflective or transparent.
Such a compass construction simplifies introduction of feedback signals because it is required only to rotate the compass case to move the sensor while the rudder is positioned to hold the boat on the desired course. A leading tiller controller is arranged so that the sensor is moved manually relative to a magnetic heading defined as the dividing line between the transparent and the opaque portion of the compass card. The compass case, and therefore the sensor, is moved relative to the compass card as the boat turns to the desired heading.
The output element of the mechanism is an apparatus which moves to move the rudder. The feedback circuit is arranged such that movement of the output element moves the sensor relative to the card. Such a servo-mechanism can be made in very simple and reliable form. Easily placed in operation and removed, it is a very convenient apparatus. Unfortunately, the degree of rudder movement and the interval over which heading correction is accomplished varies greatly. These handling characteristics vary with hull length and design and rigging and weight, and with keel design and other factors.
Each boat design dictates a different degree of feedback or "stiffness" in the servo-mechanism design. The error signal in the simple system does not vary in proportion to magnitude of error. It has one value for error to port, another for zero error, and the third for error to starboard. Changing the feedback factor electrically is possible, but costly. Conventional systems employ a system of pulleys or gears or travelling nuts and the like in moving the output and feedback elements. The degree of feedback the ratio of feedback element movement to output element movement is made a function of pulley or gear size and is changed by changing size.
That gives rise to three major problems. The first arises because it is difficult in such a structure to make the steering device equally applicable to steering from starboard or port of the tiller or wheel. The second is that distribution and sale of such automatic steering devices is made difficult by the need to install a pulley that most nearly matches the handling characteristics of the boat in most conditions. The third problem is that there is no convenient way to alter the degree of feedback to meet changing conditions. Changing the degree of feedback requires changing pulleys.